1. Field of the Invention
The present invention relates generally to a microstrip antenna for use on a weapons system to receive GPS data from an external source. More specifically, the present invention relates to a reduced size GPS microstrip antenna which has a slot, receives GPS data from an external source and which is adapted for use in a small area on a weapons system such as a missile.
2. Description of the Prior Art
Microstrip antennas are currently be used by weapons system, such as missiles, to receive GPS (Global Positioning System) data from external sources such as satellites. This GPS data is transmitted via an RF carrier signal from the satellites to the weapons system.
Microstrip antennas typically operate by resonating at a selected frequency. The design of such antennas normally makes use of printed circuit board techniques which includes a dielectric substrate which has a printed copper patch mounted on its top surface and a copper ground plane mounted on its bottom surface. The frequency at which the microstrip antenna operates is approximately a half-wavelength in the microstrip medium of dielectric below the copper patch and air above the copper patch.
Generally, microstrip antennas used by weapons system to receive data have required considerable space on board the weapons system. To reduce the physical size of the microstrip antenna, prior art antenna designs have incorporated dielectrics with high dielectric constants. Since the wavelength for the antenna is approximately inversely proportionate to the dielectric constant, the size of the antenna is reduced for an increase in the dielectric constant. Unfortunately, there is a reduction in the bandwidth of the antenna with an increase in the dielectric constant. Further, there is a cost element associated with an increase in dielectric constant in that the dielectric material is more expensive.